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Alan Stern calls these satellite planets, although the term major moon is more common. The smallest natural satellite that is gravitationally rounded is Saturn I Mimas (radius 198.2 ± 0.4 km). This is smaller than the largest natural satellite that is known not to be gravitationally rounded, Neptune VIII Proteus (radius 210 ± 7 km).
The sizes and masses of many of the moons of Jupiter and Saturn are fairly well known due to numerous observations and interactions of the Galileo and Cassini orbiters; however, many of the moons with a radius less than ~100 km, such as Jupiter's Himalia, have far less certain masses. [5]
The outer planets Jupiter, Saturn, Uranus and Neptune, compared to the inner planets Earth, Venus, Mars, and Mercury at the bottom right The four outer planets, called giant planets or Jovian planets, collectively make up 99% of the mass orbiting the Sun. [ h ] All four giant planets have multiple moons and a ring system, although only Saturn's ...
The Sun, planets, moons and dwarf planets (true color, size to scale, distances not to scale) The following outline is provided as an overview of and topical guide to the Solar System: Solar System – gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly.
The Sun and planets of the Solar System (distances not to scale). The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. It formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc.
The density of matter in the interstellar medium can vary considerably: the average is around 10 6 particles per m 3, [136] but cold molecular clouds can hold 10 8 –10 12 per m 3. [ 39 ] [ 134 ] A number of molecules exist in interstellar space, which can form dust particles as tiny as 0.1 μm . [ 137 ]
A planet in the Solar System beyond the asteroid belt, and hence refers to the gas giants. Pulsar planet: A planet that orbits a pulsar or a rapidly rotating neutron star. Rogue planet: Also known as an interstellar planet. A planetary-mass object that orbits the galaxy directly. Superior planets: Planets whose orbits lie outside the orbit of ...
Wind speeds on Saturn can reach 1,800 kilometres per hour (1,100 miles per hour). The planet has a bright and extensive system of rings, composed mainly of ice particles, with a smaller amount of rocky debris and dust. At least 146 moons [33] orbit the planet, of which 63 are officially named; these do not include the hundreds of moonlets in ...